Inhibiting carbon formation in metal reaction vessels



Patented Aug. 8, 1939 INHIBITING CARBON FORMATION 1N METAL REACTIONVESSELS Herbert P. A. Groll, Berkeley, Calif., assignor to ShellDevelopment Company, San Francisco, Calif., a corporation of Delaware NoDrawing. Application July 20, 1936, Serial No. 91,566

6 Claims.

This invention relates to a method of preventing or inhibitingundesirable side reactions resulting in excessive carbon formation whichnormally occur when endothermic chemical reactions involving one or moreorganic compounds are conducted at elevated temperatures in metal ormetal-lined reaction vessels wherein the reactant or reactants is/are incontact with a heated metal surface at the temperature of operm ation.

When endothermic reactions involving organic reactants, such as thecracking of hydrocarbons, the dehydrogenation of hydrocarbons, thedealkylation of aralkyl hydrocarbons and substitution products thereof,the dehydrogenation of organic oxy-compounds as primary and secondaryalcohols, the dehydration of alcohols, and the like are conducted inmetal or metal-lined reaction vessels as retorts, tubes, etc., at thehigh tempera 20 tures necessary to effect such reactions at a practicalrate, the heated metal surface in contact with the organic materialbeing acted upon exerts an undesirable catalytic influence causing sub-F stantial decomposition of the organic material with the formation ofprohibitively large quantities of carbon andihydrogen. These sidereactions resulting in excessive carbon formation are very undesirable;they materially decrease the yield of the desired product or products;they may result in the formation of suflicient carbon to close up thereaction tube in a relatively short time; and when catalysts are used toaccelerate the endothermic reaction, the formed carbon deposited uponthe surface of the catalyst material may render it inactive in arelatively short time and require frequent mechanical removal or burningof the carbon therefrom.

The carbon formed in the endothermic reactions to which this inventionrelates is due to the catalytic effect of the heated walls of thereaction vessel material; it is usually of a flufiy, soot-like type butit may be coherent and of a lustrous or graphitic form. It is, however,distinguished from r the entirely diflerent type of carbon which isformed by the condensation of tarry or asphaltic material and subsequentcoking of the condensate. It is not the purpose of the present inventionto inhibit this latter type of carbon formation.

50 It has heretofore been impossible to prevent or inhibit the excessiveformation of carbon which invariably occurs when endothermic reactionsinvolving organic materials are conducted on a technical scale. Thisexcessive carbon formation materially decreases t e u l ss andpracticality of the known endothermic processes which for reasons ofeconomy and to provide adequate heating of the reaction materialandtemperature control are usually conducted in metal or metal-linedreaction vessels.

Prior investigators have attempted to solve the problem of inhibitingexcessive carbon formation in organic cracking and dehydrogenationreactions by providing metal alloy tubes which could be used at the hightemperatures required without the interior surface thereof catalyzingcarbon formation. Numerous alloys consisting for the most part of ironor steel alloyed with one or more of the metals as vanadium, chromium,manganese, nickel and cobalt have been provided for 5 this purpose. Noneof the alloys proposed have successfully solved the problem; So far nometallic tube materials have been found which will not catalyze carbonformation at high temperatures. Some of the alloy tube materials arerelatively inactive as regards carbon formation when they are first putinto use, but the effect is not lasting, and the catalytic effect of thetube material increases with its use. Certain alloy tubes used in thecatalytic dehydrogenation of organic compounds may be employed with somesuccess for considerable periods of time but eventually the catalystloses its activity and must be regenerated. The loss of catalystactivity is in many cases, as when an activated alumina catalyst orsimilar catalyst is used, due to the deposition of carbon on the surfaceof the catalyst. The most practical way to reactivate a non-metalcatalyst which has lost its activity in this manner is to burn out thecarbon with an oxygen-containing gas while leaving the catalyst packedin the reaction tube. I have found that after such a reactivationtreatment, even the alloy tubes proposed by the art will catalyze carbonformation to a prohibitive extent.

Now, I have found that metal reaction tubes and other types of metalreaction vessels can be used in high temperature endothermic chemicalreactions involving organic compounds while carbon formation, due to thecatalytic influence of the walls of the metal reaction vessel, issubstantially avoided and in many cases entirely prevented.

In accordance with the invention, carbon formation in metal reactionvessels used in high temperature endothermic reactions of organiccompounds is inhibited or substantially prevented by treating the metalsurface of the reaction vessel which is exposed to the organic materialunder reaction conditions with substances which poison the catalyticinfluence of the metal surface and thus render it substantially inactiveas regards its tendency to decompose the organic material to carbon.

Suitable substances which have the desired poisoning effect on thereaction vessel material are the elements sulphur, phosphorus, seleniumand tellurium and compounds of these elements which, under theconditions of the particular endothermic reaction to which they areapplied, have the desired poisoning influence on the surface of thereaction vessel. A particularly suitable group of substances for mypurpose includes hydrogen sulphide, hydrogen selenide and hydrogentelluride and organic or inorganic compounds capable of forming thesehydrides under reaction conditions. The most frequently applied agent issulphur in the form of hydrogen sulphide, although organic sulphurcompounds as mercaptans, mercaptides, thioethers, polysulphides, etc.,may be successfully employed if desired.

The treatment of the interior surface of the reaction vessel may becarried out before it is put into use, or the treating agent may beadded to the organic material undergoing treatment in the requiredamount continuously or intermittently during the reaction. In somecases, it may be desirable to use both methods, that is, to pretreat theinterior surface of the reaction vessel prior to its use and thenmaintain the effect of the pretreatment by adding the required amount ofthe agent to the reaction mixture in the vessel during the execution ofthe process.

When pretreatment of the reaction vessel is resorted to, the reactionvessel may be treated with a suitable agent, as hydrogen sulphide, at anelevated temperature usually greater than about 200 C. and preferably atthe same temperature at which the endothermic reaction is to 40 beconducted therein. The time and temperature of the pretreatment will bedependent upon the particular treating agent used, the concentration inwhich it is employed and the characteristics of the metal surfacetreated, such as its stability to the treating agent. When the treatingagent is hydrogen sulphide, the pretreatment generally requires fromabout 5 minutes to about 120 minutes depending upon the temperatureemployed. Care must be taken to avoid excessive corrosion of thereaction vessel when the pretreatment is effected at high temperatures.For reasons of economy and to avoid excessive corrosion of the reactionvessel material, we prefer to effect the pretreatment with the minimumpractical amount or concentration of the treating agent.

After the pretreatment, the treated reaction vessel is used for thereaction proper until the passivation or catalyst poisoning effect ofthe agent with which it was treated becomes ineffective and carbonformation is again catalyzed to an undesirable extent. This conditionmay be detected in a variety of ways: the reaction tube, for example,may start to become plugged with carbon; more hydrogen may be formedthan when the reaction is proceeding while carbon formation is beinginhibited, and, when the endothermic reaction is effected in thepresence of a catalyst, a decrease in activity of the catalyst may benoted due to deposition of carbon on the surface thereof. When theeffect of the pretreatment has worn off to the extent that carbon isformed in prohibitive amounts, the reaction vessel may be taken out ofservice and again pretreated as described. In some cases, successivepretreatment of the reaction vessel is mnecessary. When the passivationof the reaction vessel surface becomes ineffective, the requireddegree-of passivation may be restored and maintained by continuouslyorintermittently adding an effective amount of the tube poisoning agent tothe reaction mixture, usually in admixture with the organic materialundergoing treatment. The length of time that the pretreated reactionvessel is ineffective. to substantially catalyze carbon formationusually depends on the nature of the metal surface of the reactionvessel, upon the temperature at which the endothermic reaction iseffected therein, and upon the nature of the reaction participants.Usually alloyed steels, lower temperatures and reaction mixturessubstantially devoid of hydrogen allow the use of less of the carbonformation-inhibiting agent and cause a pretreatment to last longer.

In general, when carbon formation is inhibited by adding the agent whichpoisons the catalytic influence of the metal surface of the'reactionvessel during the reaction, the amount of the effective agent which mustbe added to the reaction mixture or to the organic material treated willdepend upon the nature of the metal reaction vessel surface in contactwith the reactants under reaction conditions, upon the temperature atwhich the endothermic reaction is effected, and upon the nature of thematerials undergoing reaction. As when the reaction vessel is renderedpassive by pretreatment, the carbon formationinhibiting agent is addedto the reaction mixture in an amount just effective to substantiallyinhibit carbon formation. In other words, the minimum effective amountor concentration of such agent or material yielding it under reactionconditions is employed. The minimum effective amount is used forpurposes of convenience and economy and also to avoid excessivecorrosion of the reaction vessel.

My invention may be applied with excellent results to any endothermicchemical reaction involving organic materials which is conducted inmetal reaction vessels at high temperatures, that is, temperatures atwhich excessive carbon formation is catalyzed by the reaction tubematerials.

Such reactions are usually executed at temperatures equal to or greaterthan about 400 C. The type of carbon formation which may be inhibited bythe application of the process of my invention usually does not occur toany appreciable extent in endothermic reactions executed at temperaturesbelow about 400 C. However, when such carbon formation does occur inendothermic reactions executed at lower temperatures, the invention isapplicable to its inhibition.

My process is effective to substantially inhibit carbon formationregardless of the nature of the metal reaction vessel in which theendothermic reaction is effected. The reaction vessel may, for example,consist of or be lined with iron, steel, copper, silver, chromium,vanadium, nickel, cobalt, platinum manganese and the like or alloyscomprising a plurality of these as well as one or more other metals.'I'heheated metal surface in contact with the reactants may consist ofor comprise aluminum, for example, the endothermic reaction may beeffected in a calorized reaction vessel, 1. e., a steel or iron reactionvessel the interior surface of which has .been coated with aluminum. The

- process is very effective in inhibiting carbon formation in iron andsteel reaction tubes and also in nickel-iron-chromium, nickel-iron,nickel chromium, iron-chromium-vanadium, iron-chromium-molybdenum andvother alloys commonly in use as reaction tubes or retorts in hightemperature cracking and dehydrogenation processes. I have tested a widevariety of the metal reaction vessel materials on the market and I findthat they all catalyze carbon formation from organic materials at hightemperatures. In general, it can be said that all metal and metal alloyswhich are capable of acting as dehydrogenation agents at lowtemperatures will catalyze carbon formation at higher temperatures.

The present invention, while it finds perhaps its most important fieldof usefulness in processes involving the thermal decomposition orcracking of organic compounds and in the catalytic dehydrogenation oforganic compounds, is nevertheless generally applicable toallendothermic reactions requiring high temperatures and involving oneor more organic compounds. The reaction or reactions involved may be inthe liquid, vapor or liquid vapor phase and they may involve inorganiccompounds in addition to one or more organic compounds. Regardless ofthe nature and specific conditions of the endothermic reaction, thegeneral procedure to inhibit carbon formation in accordance withthe.principles of the invention is substantially the same.

My invention is applicable to the inhibition of carbon formation in awide variety of commercial processes involving the endothermic reactionof organic materials. The following processes are typical illustrativeexamples:

Liquid and vapor phase cracking operations wherein carbonaceousmaterials as petroleum, petroleum products, shale oils, vegetable oils,animal oils, coal, tars, asphalts, pitches, etc., are thermallydecomposed, in the presence or absence of catalysts, to saturated orunsaturated hydrocarbon materials of lower molecular weight. Forexample, cracking operations wherein petroleum oils or fractions thereofof a higher boiling range than gasoline are pyrolyzed or catalyticallydecomposed at high temperatures to lower boiling liquids of the gasolinetype.

Cracking processes wherein parafiin or paraflln type hydrocarbons arecracked to products rich in olefines or to aromatic hydrocarbons andolefine-containing gases. Processes wherein olefines are cracked andconverted to aromatic hydrocarbons as benzene, naphthalene, anthracene,toluene and the like. Processes wherein paraflin hydrocarbons and/orolefines are cracked, in the absence or presence of catalysts, toacetylene and/or acetylene type hydrocarbons.

Decomposition reactions of the class of which dealkylations are anexample, that is, processes wherein aralkyl compounds are treated athigh temperatures in the liquid or vapor phase and in the presence orabsence of catalysts and converted to less alkylated products. Forexample, the cracking of toluene to benzene, cresol to phenol, alkylquinolines to quinoline, etc.

Iehydration processes wherein organic oxycr wounds are dehydrated,usually in the vapor plase at high temperatures in the presence ofdehydrating catalysts. For example, processes involving the dehydrationof the aliphatic alcohols as ethyl, propyl, butyl, isobutyl, secondarybutyl, tertiary butyl, amyl, hexyl and the like to olefines and/ordioleflnes at elevated temperatures in the presence of catalysts asalumina, ceria, thoria, acidic solid salts, etc.

Decarboxylation processes involving the pyrolytic or catalytic elimationof carbon dioxide from organic carboxy compounds as carboxylic acids andcarboxylic acid esters. The process is also applicable to the inhibitionof carbon formation catalyzed by the heated interior metal surface inwhich endothermic reactions involving the formation or reaction ofcarbon monoxide are executed.

Dehydrogenation processes involving the pyrolytic or catalyticelimination of hydrogen from organic compounds. For example, processeswherein hydrocarbons of the parafiln series are dehydrogenated to thecorresponding olefines, as ethane to ethylene, propane to propylene,normal butane to n-butylene, isobutane to isobutylene, cyclohexane tocyclohexene, ethyl benzene to styrene, etc., by contact with a metal ormetal det ydrogenation catalyst at an elevated temperaure.

Processes wherein primary or secondary alcohols are contacted atelevated temperatures with metallic or non-metallic catalysts anddehydrogenated to the corresponding aldehydes or ketones, respectively.For example, processes wherein ethyl alcohol is dehydrogenated toacetaldehyde, isopropyl alcohol to acetone, secondary butyl alcohol tomethyl ethyl ketone, methallyl alcohol to methacrolein, bomeol andisobomeol to camphor, cyclohexanol to cyclohexanone, fenchyl alcohol tofenchone, and the like.

When my invention is used to inhibit the excessive formation of carbonwhen hydrocarbon or hydrocarbon mixtures are cracked in metal tubes assteel or steel alloy tubes, 1 preferably pretreat the metal tube withhydrogen sulphide at about the temperature at which the crackingoperation is to be conducted. The material subsequently treated in thepretreated metal tube may or may not contain a suflicient concentrationof hydrogen sulphide or organic sulphur compounds capable of forminghydrogen sulphide under the conditions of the cracking process tosubstantially maintain the passivity of the metal tube surface. Afterthe pretreatment accorded the metal cracking tube becomes ineilective toprevent substantial carbon formation as indicated by formation of morehydrogen than during the normal crack: ing period, the tube may be takenout of operation and again subjected to a treatment with hydrogensulphide.

My invention may be applied to the inhibition of carbon formation incatalytic dehydrogenation reactions conducted in metal reaction tubes ina variety of manners depending upon the particular dehydrogenationreaction, the specific catalyst or catalyst composition used and, uponthe nature of the reaction tube material.

The invention may be applied with excellent results to the inhibition ofcarbon formation in organic dehydrogenations carried out in metal tubesin the presence of catalysts which are not poisoned by the elementssulphur, phosphorus, selenium and tellurium and compounds thereof, orwhich have a certain tolerance for such elements and their compounds.The sulphactive catalysts as molybdenum sulphide are examples ofcatalysts which are not poisoned by sulphur and sulphur compounds ashydrogen sulphide, mercaptans, etc. There are numerous dehydrogenationcatalysts which although not immune to poisoning by the carbonformation-inhibiting agents, as for example hydrogen sulphide, have acertain tolerance for such catalyst poisons. A group of suchdehydrogenation catalysts includes among others activated alumina,activated charcoal, silica gel, magnesite, zinc oxide, chromium oxide,thorium oxide, alumina impregnated with chromium oxide, aluminaimwithout substantial loss of activity than is required to substantiallyobviate the tendency of the tube material to catalyze carbon formation.It is seen that the carbon formation-inhibiting agent may be added tothe reaction mixture in a controlled amount sufficient to substantiallyinhibit carbon formation but insufficient to materially decrease theactivity of the catalyst. For example, when using a brass catalystpacked in iron, steel or steel alloy tubes for the dehydrogenation ofalcohols, I have found that the brass catalyst can tolerate up to about0.0025% of sulphur in the alcohol treated without a substantial decreasein activity of the catalyst. In accordance with the present invention, Imay add suflicient sulphur, preferably in the form of hydrogen sulphide,to the alcohol to be treated so as to maintain the concentration ofsulphur in the reaction mixture not greater than about 0.0025% sulphur,and thus completely prevent carbon formation without deieteriouslyeffecting the life and activity of the catalyst. The above is given forpurposes of illustration only. A wide variety of other metal and metalalloy catalysts having a sufficient tolerance for the carbonformation-inhibiting agents may be used for the dehydrogenation ofalcohols and other organic oxycompounds as well as hydrocarbons. Thetolerance of the catalyst for the particular carbon formation-inhibitingagent can be readily determined and the material of the reaction vesselso selected that carbon formation can be inhibited without deleteriouslyeffecting the activity of the catalyst. The catalyst should be capableof tolerating a greater amount of the carbon formation-inhibiting agentthan is required to render the metal reaction surface incapable ofinhibiting substantial carbon formation.

My invention is applicable with excellent results to the inhibition ofcarbon formation in processes wherein hydrocarbons are dehydrogenated bycontact with solid catalysts contained in metal reaction tubes atelevated temperatures generally in the range of from about 400 C. toabout 900 C. and preferably from about 500 C. to 800 C. If the catalystused can tolerate a concentration of the selected carbonformation-inhibiting agent, for example, hydrogen sulphide, greater thanthe minimum concentration of said agent effective to inhibit carbonformation to the desired extent, pretreatment of the metal tube alonemay be resorted to, or the tube as well as ,the catalyst may bepretreated and the effect of the pretreatment maintained by providing aneffective concentration of the carbon formation-inhibiting agent in thereaction mixture during the dehydrogenation reaction.

In the dehydrogenation of isobutane, normal butane and otherhydrocarbons by contact with catalysts as activated alumina, impregnatedactivated alumina, activated charcoal, chromium oxide, and the likepacked in iron, steel or steel or iron alloy tubes, such as steel tubescontaining from 4% to 6% lybdenum, I have found that an amount of about0.3% sulphur added to the material to be treated is effective to inhibitcarbon formation for indefinite periods of continuous operationdepending only on the life of the catalyst. For pretreatment, a 10minute treatment of the interior surface of the catalyst tube withconcentrated hydrogen sulphide at the temperature at which thedehydrogenation is to be effected, is usually effective to inhibitcarbon formation during the complete life-time of the catalyst betweenregeneration treatments. With such pretreated tubes, carbon formationhas been substantially prevented for a period of as long as one week ofcontinuous operation, after which time the catalyst employed usuallyloses suflicient activity to require regeneration.

The following examples illustrate specific embodiments of my invention.It is to be understood that the examples are illustrative'only and arenot to be regarded as limiting the scope of the invention.

Example I When propane to which about 2% of hydrogen sulphide had beenadded was passed through a clean reaction tube of the same material andsize at about the same space velocity, the propane was cracked tomethane and ethylene and good yields of aromatics were obtained attemperatures of from about 700 C. to 900 C. while substantially nocarbon was formed even after the process had been operated for a longperiod of time.

Example II A reaction tube of the material and size described in ExampleI was pretreated as follows: The tube was heated to a temperature ofabout 700 C. while a stream of hydrogen sulphide was passed through itslowly for about 30 minutes.

Following the pretreatment, the tube was heated to a temperature of fromabout 700 C. to 900 C. and propane was passed through it at a velocityof about 60 c. c./min. Cracking of the propane took place without carbonformation. At 850 C., about 20% by weight of the cracking stock wasconverted to a tar which consisted of aromatic hydrocarbons, principallybenzene.

Example III Substantially pure propylene was passed through a steelreaction tube heated to a tempeirature of from about 700 C. to 900 C. Noaromatic hydrocarbons were formed but carbon formation occurred sorapidly and to such an extent that the tube was almost completelystopped up in a short time.

When propylene to which about 0.38% of hydrogen sulphide had been addedwas passed through the same clean reaction tube heated to chromium and0.2% mo-.

a temperature of about 800 0., conversion took place with substantiallyno formation of carbon. About 40% by weight of the propylene wasconverted to a tar consisting for the most part of aromatichydrocarbons.

Example IV v A clean, new steel tube of the same material as thatdescribed in Example III was pretreated as follows prior to its use forthe cracking of propylene.

The steel tube was heated to a temperature of 800 C. while hydrogensulphide was passed slowly through it for about minutes. Propylene wasthen passed through the pretreated tube heated to a temperature of about300' C. Conversion took place with practically no carbon formation. Atar of aromatic nature was formed in the amount of about 62 pounds per1000 cu. ft. of propylene passed through the pretreated tube. Thebeneficial efiect of the pretreatment of the tube lasted for more than16 hours of continuous operation. The eiliuent non-condensed gasescomprised about 15.0% ethylene, 9.9% hydrogen and 74.4% methane.

Example V A stove oil was subjected to a vapor phasel cracking treatmentby passing it through a heated steel alloy tube the material of whichcontained about 4% to 6% chromium and about 0.5% molybdenum. The processwas executed at a temperature of about 800 C. At first cracking waseffected and a naphthalene tar was obtained while but little carbon wasformed. After the tube had been in use for a short time, its interiorsurface suddenly became very active and the treated oil was decomposedto carbon, hydrogen and methane with the formation of only traces ofnaphthalene.

When the same reaction tube was originally used under the sameconditions to crack the same stock of stove oil to which about 1.0% ofhydrogen sulphide had been added, the process could be conductedindefinitely to obtain good yields of naphthalene tar with substantiallyno formation of carbon. At a temperature of 800 0., each barrel of oiltreated yielded about 42% by weight of an aromatic tar and about 2800cu. it. of a gas having an oleflne content of about Substantially thesame results were obtained when a substantially sulphur-free oil wastreated in the same reaction tube which had been previously treated withsulphur Vapor. The pretreatment of the tube was effected by heating itat a temperature of about 800 C. for about 10 minutes with its interiorsurface in contact with sulphur vapor diluted with nitrogen. Thebeneflcial effect of the pretreatment lasted for about hours after whichtime the tube was taken out of service and again pretreated and thiscycle repeated about every 20 hours.

The same beneficial results were obtained when the tube was pretreatedas described with dimethyl sulphide instead of sulphur vapor.

Example VI I Metal reaction tubes were pretreated as described inExample IV with the vapors of phosphorus, hydrogen selenide and hydrogentelluride, respectively. These pretreated metal tubes were used forpropylene cracking under the conditions described in Example IV. Thetube pretreated with phosphorus was used without carbon formation forabout 26 hours. The tubes treated with hydrogen selenide and hydrogentelluride were inactive for correspondingly long periods of time.

Example VII A brass catalyst was packed in a steel catalyst tube havingan inside diameter of about The tube was heated to a temperature of fromabout 425 C. to about 495 C. over a length of about 17" while pureisopropyl alcohol was passed through it at a rate of about 600 c. e. perhour. For the first few hours, the conversion of isopropyl alcohol toacetone was about 80%; it then began to drop off rapidly indicating adecrease in activity of the catalyst. It was found that considerablecarbon had been formed and that the loss of activity of the catalyst wasdue to deposition of carbon on the surface thereof, said carbonformation being catalyzed by the material of the reaction tube.

A clean reaction tube of the same material and size and packed with thesame catalyst as abovedescribed was used under the same conditions oftemperature, and isopropyl alcohol 'to which about 0.0025% of sulphur inthe form of hydrogen sulphide had been added was passed through theheated tube at a velocity of about 600 c. c./hr. The process wasoperated continuously for about 56 hours during which time theconversion of isopropyl alcohol to acetone was about 80%. At the end ofthis time, examination of the catalyst showed that substantially nocarbon had been formed.

Example VIII Isopropyl alcohol containing about 0.005% sulphur waspassed over a new brass catalyst packed in a steel tube of the samematerial and size as described in Example VII. The tube was heated to atemperature of from about 450 C. to 500 C. while the isopropyl alcoholwas passed through it at a rate of 600 c. c./hr. The conversion ofisopropyl alcohol to acetone was about 80% throughout the first 18 hoursof operation, but it gradually decreased until it was only about 50% atthe end of 24 hours, thus indicating a progressive decrease in catalyticactivity. The operation was terminated and the catalyst examined.Substantially no carbon formation had occurred. The loss of activity ofthe catalyst was due to the use of an amount of the carbonformation-inhibiting sulphur greater than could be tolerated by thecatalyst without loss of activity.

The catalyst was reactivated by passing substantially sulphur-freeisopropyl alcohol through the tube under reaction conditions for about 5hours, during which time the conversion rose to about 80%. The cycle wasrepeated as necessary to maintain the activity of the catalyst.Throughout the operation, carbon formation was substantially avoided.

Example IX Isobutane was dehydrogenated to isobutylene by passing it inthe vapor phase through a heated steel reaction tube packed withgranules of an activated alumina catalyst. The temperature of thecatalyst tube was maintained at about 600 C. and the space velocity ofthe isobutane through it was about 198. The dehydrogenation occurred toform isobutylene but after a short time the walls of the reaction vesselbecame so active that the treated isobutane was decomposed to carbon,hydrogen and methane exclusively.

When the same reaction tube and catalyst was used under the sameconditions as abovedescribed to dehydrogenate isobutane to which about0.5% of hydrogen sulphide had been added, a 35% to conversion of theisobutane to isobutylene was maintained over a period of 24 hoiirs orlonger without substantial carbon formation or loss of activity of thecatalyst.

Example X A steel reaction tube was packed with granules of an activatedalumina and pretreated with hydrogen sulphide in the following manner:

The packed tube was heated to a temperature of about 600 C. whilehydrogen sulphide was passed through it slowly for a period of about 30minutes. I

The pretreated reaction tube was used to eflect the dehydrogenation ofnormal butane. The butane was passed, at a space 'velocity of about 198,through the tube maintained at a temperature of about 600 C. An averageconversion of about 30% of the butane to butylene was maintained over along period of time while substantially no carbon was formed.

The term space velocity as used in the above examples may be defined asthe number of units ofvolume of gaseous material, measured at 0 C. and76 cm. of mercury, contacted with a unit volume of catalyst per hour.

While I have described my invention in a detailed manner and providedspecific examples illustrating suitable modes of executing the same, itis to be understood that modifications may be made and that nolimitations other than those imposed by the scope of the appended claimsare intended.

I claim as my invention:

1. In a process for the catalytic dehydrogenation of organic compoundsin the vapor phase to valuable organic products containing fewerhydrogen atoms in metal reaction vessels at elevated temperatures, atleast equal to about 400 C., the method of inhibiting the formation ofnon-asphaltic type carbon catalyzed by the reaction tube material whichcomprises pretreating the interior surface of the reaction tube withhydrogen sulphide at an elevated temperature greater than about 200 C.for a time adequate to poison the metallic surface and render itsubstantially inactive to catalyze carbon formation under the conditionsat which the dehydrogenation is effected and executing said catalyticdehydrogenation reaction wherein dehydrogenation predominates andcracking is substantially obviated.

2. In a process for the catalytic dehydrogenation of organic compoundsin the vapor phase to valuable organic products containing fewerhydrogen atoms in metal reaction tubes, at least equal to about 400 C.,the method of inhibiting the formation of non-asphaitic type carbonwhich comprises effecting the dehydrogenation in the presence of adehydrogenation catalyst which is substantially active to catalyzedehydrogenation in the presence of an amount of hydrogen sulphide,adequate to render the reaction tube material in contact with thereaction mixture sub stantially inactive to catalyze carbon formationunder the conditions of the dehydrogenation, and maintaining in thereaction mixture during the dehydrogenation a minimum amount of such acarbon formation-inhibiting agent effective to keep the interiormetallic surface of the reaction tube poisoned and substantiallyinactive to catalyze carbon formation and executing said catalyticdehydrogenation reaction wherein dehydrogenation predominates andcracking is substantially obviated.

3. In a process for the dehydrogenation of a non-tertiary alcohol to thecorresponding carbonylic compound in the presence of a brass catalystcontained in a steel reaction tube and heated to a temperature of about500 0., the method of inhibiting the formation of non-asphaltic typecarbon catalyzed by the interior surface of the reaction tube whichcomprises maintaining in the treated alcohol a minimum concentration ofhydrogen sulphide effective to inhibit carbon formation by poisoning theinterior surface of the metal reaction tube but ineffective to cause anysubstantial decrease in activity of the catalyst and executing saidcatalytic dehydrogenation reaction wherein dehydrogenation predominatesand cracking is substantially obviated.

4. In a process for the catalytic dehydrogenation of a paraffinhydrocarbon to the corresponding hydrocarbon containing fewer hydrogenatoms in the presence of an activated alumina mtalyst contained in asteel reaction vessel heated to. a temperature of from about 400 C. to,bout 900 C., the method of inhibiting the formation of non-asphaltictype carbon catalyzed by the interior surface of the reaction vesselwhich comprises maintaining in the reaction vessel during thedehydrogenation a concentration of hydrogen sulphide effective toinhibit carbon formation by poisoning the interior surface of the metalreaction vessel but not sufficiently high to cause any substantialdecrease in activity of the catalyst and executing said catalyticdehydrogenation reaction wherein dehydrogenation predominates andcracking is substantially obviated.

5. In a process for the catalytic dehydrogenation of isobutane toisobutylene in the presence of an activated alumina catalyst containedin a steel alloy reaction tube and heated to a temperature of from about500 C. to about 800 C., the method of inhibiting the formation ofnon-asphaltic type carbon catalyzed by the interior surface of thereaction tube which comprises adding hydrogen sulphide to the treatedisobutane in an amount sufficient to maintain a concentration of about0.5% hydrogen sulphide in the reaction mixture in the reaction tubeduring the dehydrogenation and executing said catalytic dehydrogenationreaction wherein dehydrogenation predominates and cracking issubstantially obviated.

6. In a process for the catalytic dehydrogenation of a butane tobutylene in the presence of an activated alumina catalyst contained in asteel alloy reaction tube and heated-to a temperature of from about 500C. to about 800 C., the method of inhibiting the formation ofnonasphaltic type carbon catalyzed by the interior of the reaction tubewhich comprises pretreating the reaction tube packed with the catalystby heating it to a temperature of about 500 C. to about 800 C. andpassing hydrogen sulphide through it for a time adequate to poison theinterior surface of the reaction tube and render it substantiallyinactive to catalyze carbon formation during the execution of thedehydrogenation reaction and executing said catalytic dehydrogenationreaction wherein dehydrogenation predominates and cracking issubstantially obviated mmnnar P. A. anoin-

